This invention relates to an articulated support structure for selectively positioning a lamp head over a drafting board to illuminate selected areas of the board to facilitate a draftsman's work. A drafting lamp structure is usually supported at the upper edge margin of a drafting board to occupy as little surface area of the board as possible. The articulated arm structure of such a lamp is required to reach all extremities of the board while maintaining a desired height above the board surface to minimize interference with the draftsman's hands, arms, and head while drawing. A standard board is usually about 371/2 in vertical dimension and in lateral dimension may vary from 50 inches to 72 inches.
Prior proposed lamp structures have included various arrangements of articulated arms. One prior proposed lamp structure included telescopically arranged lamp supporting members pivotally connected to a base clamped on the edge of the board. Another prior proposed lamp support included pivotally interconnected parallelogram arm arrangements in which upper and lower support arms were each biased by independent springs extending from adjacent their pivotal connections to a point intermediate ends of the respective arms. Another prior proposed drafting board lamp supporting structure is disclosed in U.S. Pat. No. 2,299,251 and another embodiment thereof in U.S. Pat. No. 2,200,518. In each of these patents, a counterbalancing torsion spring is mounted in a base assembly adjacent the clamping of the base assembly to the drawing board. A linkage system is connected in force transmitting relation to the torsion spring, the linkage system extending along a lower support arm in generally spaced parallel exposed arrangement for connection at its upper end to the upper support arm. The linkage system is connected to a link pivoted on the base assembly and having an end extending externally of the base housing to transmit the biasing forces to the parallel link extending along the lower support arm.
In the above-mentioned prior proposed lamp supporting structures, the overall horizontal reach of the articulated arms extended from about 36" to 42" when the drafting board was in horizontal position and in vertical position extended only from about 16" to 24" from the top edge margin of the board because of the construction of the base assembly.
It should be noted that in some countries many draftsman prefer to draw with the board in horizontal or in an inclined position; whereas in other countries such as some of the European countries, draftsmeh prefer to draw with the board in substantially vertical position. It thus becomes apparent that the support structure for a drafting table lamp should be capable of illuminating areas of a drafting board when the drafting board is not only in horizontal or inclined position, but also in a vertical position. The prior proposed lamp supporting structures mentioned above had only limited capability in satisfying the demands for stable fixed support of a lamp head adapted to selectively illuminate a drawing board surface in vertical, inclined, and horizontal positions of the drafting board.